Using M-mode echocardiography, an estimate of left ventricular filling pressure in critically ill patients was calculated by determining the ratio of the time the onset of the QRS complex on EKG to mitral valve closure and the time from aortic valve closure to mitral valve E-point. Using linear regression, an equation was derived that provided an estimate of pulmonary capillary wedge pressure. This estimate was compared to the pulmonary capillary wedge pressure measured by standard techniques using a pulmonary artery catheter, and a strong correlation was found. Serial studies in individual patients showed a good correlation of echo-determined pulmonary capillary wedge pressure with pulmonary artery catheter-determined pressure may allow some patients to be managed with a shorter duration of pulmonary artery catheterization and may decrease the need for repeated catheterization in some patients.